The Effects of Strong and Weak Acids on the Order of a Reaction.

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Introduction

Aim To investigate the effect strong and weak acids have on the rate of a reaction and its order. Introduction What is a chemical reaction? This is the first question that needs to be answered before tackling this investigation. A chemical reaction is the process which results in the chemical conversion of one substance into another. These reactions can be placed into two groups; exothermic and endothermic reactions. If the energy given out of the reaction is greater than the energy taken in, the reaction is known as an 'Exothermic Reaction'. Similarly, if the energy taken in is greater than the energy given out, the reaction is known as an 'Endothermic Reaction'. The easiest way to determine if a reaction is Exo/Endothermic is to observe any temperature changes within or after the reaction has taken place. If the surrounding temperature drop, the reaction is exothermic and if the temperature increases, the reaction is exothermic. Although it is true that every substance has the potential to be converted into another, it is also true that before a reaction happens, certain criteria needs to be met. For a reaction to happen, the particles must collide with the correct amount of energy - also known as the 'Activation Energy'. The Activation energy is the lowest amount of energy a particle needs in order for it to successfully collide with another and for the reaction to take place. So, for a reaction to 'go', a certain number of particles have to have the correct amount of energy. Although the activation energy for a reaction can never be changed, outside factors can affect how many particles in the reaction have the minimum energy requirement to react successfully. Figure 1: http://www.docbrown.info/page03/3_31rates.htm#3a As you can see from the above diagrams, the Activation energy (Ea) is the difference between the transition state of the particles - the state where the old bonds aren't yet fully broken and the new bonds aren't yet fully formed. ...read more.

Middle

The beginning of the reaction between the Magnesium Ribbon and the acid was very fast and the slowed down towards the end. It is the beginning which is crucial in finding the initial rate of the reaction, so I decided to decrease the time intervals so I was able to get better results. Activation Energy For the Activation Energy experiments I had to first find the volume of gas that was the most appropriate to measure. For this, I had to do the experiment with HCl and C2H3OOH at a high and low temperature. This was so that I can find a volume which suited both's initial rates of reaction. HCl - Time (s) Volume (cm�) at 20� 0 0 5 6 10 10 15 14 20 18 25 21 30 24 35 25 40 26 45 28 50 29 55 30 Time (s) Volume (cm�) at 70� 0 0 5 16 10 21 15 25 20 28 25 30 30 32 35 34 40 37 45 39 50 40 C2H3OOH - Time (s) Volume (cm�) at 20� 0 0 5 2 10 5 15 7 20 10 25 14 30 20 35 23 40 26 45 30 50 33 55 36 60 39 65 42 70 45 75 51 80 53 85 56 90 57 Time (s) Volume (cm�) at 70� 0 0 5 10 10 22 15 35 20 45 25 55 30 60 35 67 40 72 45 76 50 78 55 78 I then drew a graph to illustrate the date above and worked out a suitable amount of Hydrogen gas to measure: After drawing the graphs and finding suitable volumes to measure for each, I had to decide which temperature I wanted it to be measured at. My initial though was every 20 degrees: 20 �, 40 �, 60 � and 80 �. After a test run for each temperature, I found that these temperatures were perfect to use. ...read more.

Conclusion

This is a very large change and could account for some of the errors made. Another error I found was not sealing the system fast enough. This was most apparent when using the highest temperatures and during the preliminary experiments with the Magnesium Powder. Not getting the bung on quickly enough meant that some of the gas escaped before being sealed in the syringe and so the initial rate of the reaction would be skewed. As the reaction in higher temperatures happened rather vigorously, once the first few seconds have passed, the reaction may have reached its peak already. Not sealing the tube quickly enough would mean that an accurate reading of the results wouldn't have been possible to obtain. If I were to conduct this experiment again, there would be some errors that could possibly be eliminated. Getting another person to start the stop-clock whilst I drop the Magnesium into the reaction and seal it with a bung would be the first correction. This would severely reduce the amount of gas which had escaped from the system in my previous experiment. The Oxide layer coating the Magnesium, although previously sanded, would have inevitably built up during the course of the experiment. Sealing the pieces in an air-tight container would reduce any reaction from occurring before the pieces are used. Using a burette to measure out the acid volumes rather than a measuring cylinder would definitely make the quantities more accurate and the results more reliable. Using water baths like I had previously to keep the temperature constant would be used again to stop any outside temperatures from affecting the rate of the reaction. I would also change my experiment slightly and use Mono and Dibasic acids instead. This way, I could potentially see whether two strong acids with a different number of acidic Hydrogens react differently and affect the order and activation energy significantly. Using Sulphuric acid and Hydrochloric acid would be my choice. ?? ?? ?? ?? Chemistry Coursework The Effects of Strong and Weak Acids. 1 ...read more.

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